Xerographic apparatus with endless development electrode



July 15, 1958 R. E. HAYFORD XEROGRAPHIC APPARATUS WITH ENDLESSDEVELOPMENT ELECTRODE A 2 Sheets-Sheet 1 Filed June 16, 1955 VACUUM HIGHPOTENTlAL SOURCE CLEANER DEVELOPER'VZS SUPPLY INVENTOR RICHARD E.HAYFORD ATTORNE July 15, 1958 RD 2,843,084 XEROGRAPHIC APPARATUS WITHENDLESS 7 DEVELOPMENT ELECTRODE Filed June 16, 1955 2 Sheets-Sheet 2DEVELOPER 6 CLOUD 55 62 i s u P P LY vAcuuM VACUUM 12 CLEANER CLEANER Em A a; A f

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RICHARD E. HAYFORD BYRMPAJS+ i ATTORNEY United States Patent XEROGRAPHICAPPARATUS WITH ENDLESS DEVELOPMENT ELECTRODE Richard E. Hayford,Pittsford, N. Y., assignor to The Haloid Company, Rochester, N. Y., acorporation of New York Application June 16, 1955, Serial No. 515,886

4 Claims. (Cl..118-637) This invention relates in general to xerographyand more particularly to automatic xerographic equipment.

formed on the surface of the insulating layer by exposing this layer,while sensitive, to a light pattern. Areas of the .photoconductiveinsulating layer exposed to light become more conductive than areas notexposed to light and charges on the surface of areas exposed are rapidlydissipated, whereas charges on the surface of areas not exposed remainin place. The charge pattern formed by exposure of the sensitive platemay be developed by bringing electrostatically charged particles .intocontact with the surface area carrying the pattern, or the charges maybe otherwise utilized. A developed image composed of particles depositedin conformity with the electrostatic charge pattern may be transferredfrom the surface of the plate to sheets or webs through the use ofelectrostatics or other techniques known to the art, and developedimages, whether transferred or not, may be permanently afiixed to thesurface on which they reside.

Xerography as described above may be adapted for automatic operation bycycling the xerographic plate through the various steps which producethe developed image, which may then be transferred. The cycle to producethe developed and transferred image may be repeated automatically.

A problem which has been encountered in automatic continuously operatingmachines involves an electrode used in the development stage. Thiselectrode, which will be referred to in this application as adevelopment electrode, is closely positioned while at a spaced distancefrom the surface of the photoconductive insulating layer duringdevelopment.

Basic to the use of the development electrode is the desire to reproducecopies of high quality and without distortion of the original image..Electrostatic lines of force exist between the electrostatic charges onthe photoconductive insulating layer and areas of different chargepotential. When large areas carrying electrostatic charges exist thelines of force which are present due to charges in the central area ofthe large area tend to run inward through the photoconductive insulatinglayer to the conductive backing member which is the nearest surfacecarrying a different patential. Lines of force running fromelectrostatic charges near the external boundaries of this large areawill tend to extend outward and around the outside border of the largearea at which point their paths will extend inw-ardto thephotoconductive insulating layer to an area carrying a differentpotential. De-

velopment of such an electrostatic image creates deposition whichrelates to the paths taken by the electrostatic lines of force ordevelopment of the electrostatic fields.

Therefore, development of a large area as hasjust been 'ing member.

Patented July 15, 1958 described will. produce copies with hollowcenters and emphasized edges. To prevent such development anequipotential surface is positioned at a slight distance from :thephotoconductive insulating layer during development. composed of aconductive material and is either biased :or maintained at the potentialfound on the plate back- Such an equipotential surface will cause .anincrease in the .lines of force extending outwardly from'the platemember creating electrostatic fields which when developed will producedistortion free and fringe free high quality copy.

During development fine charged powder particles are brought into thefield of influence of the charges on the surface and are deposited oncharged areas. The development electrode which is spaced at a slightdistance from the sensitive layer, tends to build up on its surface acoating of developer material. While this coating remains thin the imagewhich is developed is generally not alfected. However, a coating ofdeveloper material on the development electrode interposes a new surfacebe- .tween the sensitive layer and the development electrode. If theparticles carry electrostatic charge, this coating may effectivelychangethe bias potential on the electrode and .quickly cause theelectrode to be no longer an equipotential surface which substantiallydecreases beneficial aspects of the development electrode duringdevelopment.

This coating also adds additional and uncontrollable problems. The lackof control which follows heavy deposition is to some extent attributedto the fact that the coating which forms is generally uneven and followsunknown and different patterns. A heavy coating may :drop agglomeratesof developerpowder to the plate surface resulting in a nonuniformdistorted development of the electric image pattern. Also, such acoating may cause irregular and uncontrolled flow patterns of thedeveloper material being presented to the plate surface which will causestreaking of the developed image.

, In continuously operating. automatic machines, development isconstantly taking place, in that a new portion of a. plate carrying anelectrostatic charge pattern is continuously presented to thedevelopment zone for development purposes. It, therefore, becomesdesirable to present a development electrode above the area to bedeveloped with a minimum coating of developer particles tofacilitate'high quality true reproductions in continuously operatingautomatic machines.

It is an object of this invention to improve the art of xerography byproviding new means, methods and apparatus which relate to automaticxerographic equipment.

It is another object of this invention to improve the art of xerographyby providing new means, methods and apparatus which relate 'to thedevelopment electrode.

It is a'further object of this invention to devise and disclosemechanism to provide for presentation of a development electrodecarrying a minimum coating of developer particles over areas to bedeveloped on a xerographic plate.

It is yet a further object of this invention to devise .new methods toclean all areas of the developmentelectrodeused in a machine forcontinuous operation during each successive cycle of movement of thedevelopment electrode.

Other objects and advantages of this invention will be apparent in viewof the following description considered in the light .of the attacheddrawings, wherein:

Fig 1 is. aschematic view of one embodiment of an automaticelectrophotographic device adapted for continuous operation.

Fig. 2 is a diagrammatic view of another embodiment of exposureaccording to this invention.

This'surface, the development electrode, is

Fig. 3 is a diagrammatic view of one embodiment of a development zoneaccording to this invention.

Fig. 4 is a diagrammatic view of another embodiment of a developmentzone according to this invention.

Fig. 5 is a cross'section viewtaken along line 55 of Fig. 4.

Referring more specifically to the drawings, in Fig. 1 is shown anembodiment of a continuously operating xerographic machine. Axerographic plate generally designated formed in the shape of a drum isadapted to be rotated in the direction indicated. Rotation may bebrought about through the use of normal driving techniques, such asmotors or the like. In this figure, driving is accomplished by motor 14through belt 19. The plate 10 is composed of a conductive backing member11 which, as is illustrated, is held at a ground potential, and aphotoconductive insulating layer 12. on the inner surface of the drum. Auniform electrostatic charge is placed on layer 12 by corona dischargeelectrode 13 supplied with high potential corona generating voltage fromhigh potential source 15. Generally from 6000 to 8000 volts will besufiicient to create corona discharge. It is to be realized, of course,that other means for placing an electrostatic charge on the surface ofthe photoconductive insulating layer 12 may be used and are intended tobe encompassed by this invention as for example radioactive charging,frictional charging, or the like. The drum is moved following chargingto an exposure station generally designated 16. In this embodiment, aprojector 17 throws light from light 18 through film 20. The pattern oflight passing through the film is then projected through lens 21 andonto the surface of the photoconductive insulating layer 12. The film issupplied from film supply spool 25 and is moved, as indicated, at aproper linear speed through slit area 23 and to film wind-up spool 22.Slit projection is used in this embodiment to avoid distortion informing the image on the curved surface of photoconductive insulatinglayer 12, but other techniques known to those in the art may be used.The film 20 is driven by normal driving mechanism, such as a motor orthe like, synchronized to the linear speed of the drum or otherwisecontrolled to bring about proper speed for continuous projection ofcontinuously moving copy to be reproduced on a continuously moving drum.Although projection type of exposure is shown in this figure, it is tobe realized that other types of exposure may be used, as for examplereflex exposure, contact exposure, and the like, and such means ofexposure are intended to be included in this invention. Also it is notedthat since exposure is to the inner surface of the drum, it may bedesirable to create the slit light pattern to be projected to the innersurface of the drum at an area external of the drum. This may beaccomplished through the use of prisms positioned to focus the slitlight pattern on the inner surface of the drum, whereas the projector orreflex mechanism or the like is positioned externally.

Next in position of movement of the inner surface of the drum isdevelopment station 26. This station comprises development electrode 27,developer supply 28, and conveying means to convey the developer supplyto the area between developement electrode 27 and the surface ofphotoconductive insulating layer 12. At development station 26development of the electrostatic charge pattern formed at exposurestation 16 takes place. Developer supply 28 may supply a cloud ofdeveloper particles in gas to the area carrying the charge pattern fordevelopment purposes, or other known techniques of development may beused, as for example, it is intended to include within the scope of thisinvention development of the electrostaic charge pattern through the useof cascade development commonly used in the art of xerography. Cascadedeveloping is disclosed in Walkup U. S. Patent 2,618,551.

Following development, the plate 10 is next moved 4 to a transferstation generally designated 31. Various transfer techniques may beused. In this embodiment, adhesive type of transfer is illustrated. Asupply roll 32 of adhesive coated transfer paper or other materialsupplies the transfer material. The material lS passed over roller 33,which is positioned to bring pressure to bear against the back side oftransfer material 35 to thereby press the front side of transfermaterial 35 into contact with the surface of photoconductive insulatinglayer 12 carrying the developed xerographic image. The image adheres tothe transfer material because of the adhesive coating on its surface.Roller 33 may be any type of roller which will bring pressure to bearagainst transfer material 35, as for example, a rubber coated roller orthe like. The transfer material 35 is then covered in this embodimentwith a thin, transparent cover material 36, such as cellophane or thelike, supplied from cover supply spool 37. The cover material 36 and thetransfer material 35 are pressed together between rollers 38 and 4t) andthe two materials adhere to one another because of the adhesive coatingon the surface of transfer material 35. The covered transfer material isnext fed from between rollers 38 and 40 to copy takeup spool 41. Drivingmeans, such as motors or the like, drive the transfer material 35 andthe cover mate rial 36 at a rate which is synchronized with the linearspeed of the movement of plate 10.

Although an adhesive type of transfer mechanism has been shown in thisembodiment, it is to be realized that other transfer means may be used,as for example, the developed image may be transferred through the useof corona transfer as is described, for example, in Schaffert U. S.Patent 2,576,047. The image may also be made permanent in other ways,such as for example, through vapor fusing, heat fusing, coating or thelike.

Next in the path of movement following transfer station 31 is cleaningstation 42, whereat the surface of the photoconductive insulating layer12 on which the image was formed is brushed clean by rotating brush 43or the like. Surrounding rotating brush43 is a hood 45 connected to avacuum cleaner 46, which acts to draw off removed developer or dustparticles. Plate 10 is then ready for recycling. It is also to berealized that although the cleaning means in this embodiment has beendescribed in terms of a rotating brush, other means such as a wiperblade, air knife, or the like may be used, and are intended to beencompassed by this invention.

Another exposure technique is shown in Fig. 2. In this figure, asthroughout this application, like numerals designate like elements. Inthis embodiment, drum 10 comprises a conductive backing member 47 andphotoconductive insulating layer 12. At exposure station 16, lamps 48project light to copy 50 which is reflected back through slit 51 andthrough lens 21. In this embodiment, conductive backing member 47 is atransparent conductive material, as for example, conductive transparentglass. To carry out the xerographie process, the photoconductiveinsulating material must be affected by an activating pattern, as forexample, a pattern of light and shadow to be recorded. In the embodimentof this figure the photoconductive insulating layer 12 receivesradiation through the conductive backing member which is transparent andthe light pattern affects the photoconductive insulating layer 12 at theinterface between layer 12 and the conductive backing member 47, thusbringing about exposure of the photoconductive insulating layer 12 tothe pattern of light and shadow to be recorded. As has been indicatedpreviously, other techniques of exposure are also intended to beencompassed by this invention.

Reference is now had to Fig. 3 wherein is shown in greater detail anembodiment of development stage 26. As is more clearly shown in thisfigure, the development electrodes'27 are in the shape of endless beltsand spaced so ,that the surfaces near the sensitive layer conform, as

would concentric cylinders, with the curve of the surface ofphotoconductive insulating layer 12. Thus, when portions of the endlessbelt development electrodes 27 are between positioning plates 53 and thesurface of photoconductive insulating layer 12, they conform to theshape of the near surface of the photoconductive insulating layer 12.

The endless belt development electrodes 27 are driven by rollers 52,which may be rubber rollers or the like. Rollers 52 are rotated forexample, by motor 55 through driving belt 56. Rollers 52 press againstthe back side of endless belt development electrodes 27 and thustranspose their rotation into movement of endless belt developmentelectrodes 27. At the axle of one of the rollers 52 gearing means may beprovided to bring about motion of the endless belt developmentelectrodes in the directions indicated in this figure. Other means fordriving the rollers or the electrodes generally known to those in theart are also intended to be included in this invention.

Positioned along the path of movement of endless belt developmentelectrodes 27 are cleaning means, as for example, rotating brushes 57driven by driving belts 58 and motors 66. Surrounding the rotatingbrushes 57 are hoods 61 connected to vacuum cleaners 62 throughconnecting tubes 63. The brushes '7 rotate against developmentelectrodes 2'7 and brush particles deposited during development from thesurface of the development electrode into hood 61. Particles are removedfrom the hood into vacuum cleaners 62 through connecting tubes 63.Additional connecting tubes 65 are connected to hoods 66 and negativepressure is thus supplied to the areas defining the extremes of thedevelopment station 26. A cloud of developer particles in gas issupplied from developer cloud supply 67 through conveying means 68 tothe area defined by development electrodes 27 and stops 7b, which maycomprise felt or the like, acting to close oh? the development zone andto prevent backfire of cloud supplied out the output end of conveyingmeans 68. Although the cloud is illustrated as fed normal to the plate,there is no intention to be limited thereto. It is to be realized thatthis illustration is intended to be pictorial in this respect and thatvarious means of supplying the cloud that would occur to those skilledin the art are intended to be included herein. The cloud of particles ingas supplied from developer cloud supply 67 is conveyed to the surfaceof photo-conductive insulating layer 12 beneath portions of developmentelectrodes 27. The portions of development electrodes 27 which definethe areas to which the cloud of particles in gas is supplied are thoseportions between positioning plates 53 and the surface ofphotoconductive insulating layer 12. The cloud which is supplied to theplate passes along between those portions of development electrodes 27and the surface of the photoconductive insulating layer to hoods 66,whereat particles not deposited are removed into vacuum cleaners 62.Particles, as they travel along their path of movement, deposit on theelectrostatic charge patterns carried by the surface'of thephotoconductive insulating layer 12, thereby creating the developedxerographic image. The output feed of developer supply, as isillustrated in this figure, is at a distance from the surface of thephotoconductive insulating layer. It is a distance defined on two sidesby development electrodes 27. The other two sides or edges arepreferably blocked off with similar stops such as stops 70 or the like,and the area from the output end of conveying means 68 to the surface ofthe photoconductive insulating layer 12 defines in effect a diffusionarea wherein particles in gas which may be .fed in streams or the likefrom tubes or the like diffuse to create a uniform aerosol forpresentation to the surface of the plate. Optionally thtre may be addedadditional air or the like to diffuse streams of cloud or to perfect theaerodynamics of the cloud being presented to the image carrying surface.

Although a specific direction of movement of the development electrodesis shown in this figure, there is no intention to be limited to suchmotion. Such motion, however, is preferred in that after the developmentelectrodes are cleaned by brushes 57, they are moved against stops 70whereat they are again brushed clean, and a clean electrode is thenpresented for development purposes. This electrode is presented first atthe diffusion area and then to the area where development takes place.

In Fig. 4 is shown another embodiment of development zone 26 accordingto this invention. In this figure, a single positioning plate 5.3 isused to position the endless belt development electrode 27 at a properdistance from the surface of the xerographic plate, generally designated16, which comprises backing member 11 and photoconductive insulatinglayer 12. The belt drive may be a roller 52 similar to the roller shownin Fig. 3, or it may comprise other types of friction drive generallyknown to the art. Roller 52 may be driven as is the roller in Fig. 3, orit may be driven in other ways generally known in the art. In thisembodiment developer is supplied in aerosol form from developer cloudsupply 67 through conveying tube 71 to output head 72. Output head 72comprises a chamber and a tube or nozzle 73 extending into the areawhereat development of images on the surface of photoconductiveinsulating layer 12 takes place. A plurality of nozzles or tubes may beused. Positioned at the other end of development zone 26 is a hood66connected to negative pressure generator 75 to create a negativepressure and to define a path of movement for the particles in gasfollowing passage over the area'of the plate surface to be developed. Inthis embodiment, the cleaning means is illustrated as a wiper blade 76which brushes against the surface of the development electrode 27 andremoves the particles deposited thereon during development. The wiperblade 76 is surrounded by a hood 61 and is connected through connectingmeans 63 to negative pressure generator 75. Negative pressure generator75 supplies negative pressure to draw off particles'from hood 61 removedby wiper blade 76.

Reference is now had to Fig. 5 wherein is shown a cutaway cross-sectiontaken along line 5-5 of Fig. 4. The plate designated 10 comprisingconductive backing member 11 and photoconductive insulating layer 12 isspaced from the surface of development electrode 27 by a gas gap,generally air, and development electrode 27 is positioned in physicalcontact with support plate 53. The width of the electrode is at least asWide as the surface on which. the charge pattern is formed. Extending tothe edge of the photoconductive insulating layer 12 is a stop 77 toprevent powder cloud leakage out the edges at the development zone. Sucha stop 77 acts also to create an enclosed area at the development zone,thereby allowing the creation of flow patterns which are regular duringcontinuous development. Stop 77 is permanently fastened to positioningplate 53 and may comprise felt or a similar material which will allowplate 10 to rotate freely while contacting stop 77.

When in position the development electrode should be taut. The use of aflexible material to make up the endless belt development electrode ofthis invention allows proper shaping and proper movement as the beltmoves through its cycle, which includes turns and changes of direction.By holding the electrode taut and .by using a flexible material, properspacing and positioning of the belt near the surface of the plate to bedeveloped is accomplished as the belt moves through its cycle.

The surface material of the endless belt development electrode should beat least a fair conductor of electricity, in that generally theelectrode would be biased to the potential of the plate backing memberor at a potential raised therefrom during development. Such an electrodewould include, but is not limited to, a cloth material carrying a metallayer, cloth having interspersed throughout sputtered metal or the like,a plastic belt carrying a metal layer, foil, or any flexible conductivematerial such as conductive rubber.

To assure that the development electrode is held taut according to thisinvention, while avoiding the use of other mechanism such as vacuums,magnets, or the like which would further complicate the developmentelectrode mechanism, the positioning plate which acts to hold theelectrode at a proper distance from the surface to be developed ispreferably convex. In some instances, a flat positioning plate may beused, as for example, when rollers or the like are positioned at theedges of the positioning plate to facilitate movement of the developmentelectrode. However, even when a flat positioning plate is used, it isdesirable to position the rollers or the like at the edges slightlybehind the surface of the positioning plate, and it is also desirable touse a short rather than a long plate over which the electrode travels.When using a fat positioning plate, the image carrying layer will alsobe flat.

The development electrode should be dimensionally stable and should bepolished when possible, so as to present a smooth, even equidistantsurface to the photoconductive insulating layer. Preferably thethickness of the development electrode is uniform throughout.

The positioning and drive mechanism for an electrode according to thisinvention preferably should have means to vary spacing from the surfaceof the photoconductive insulating layer and means to vary the speed ofmovement of the electrode as it passes through its cycle. Generally theelectrode is spaced from .1 to .001 inch from the photoconductiveinsulating layer and screw adjustments or the like may be connected tothe supporting elements of the positioning plate and driving roller tovary spacing from the surface'to be developed. Other means generallyknown to the art may also be used. A variable speed motor will allowsufiicient control over the speed of movement of the belt.

It is to be realized that the linear speed of the endless beltdevelopment electrode of this invention is dependent on a number offactors, such as the linear speed of the plate, the quality of copydesired, and the like. Generally faster speeds are preferred in thatportions of the plate would be carried through the entire cycle withgreater rapidity than if slower speeds were used. Preferred timing formovement of a portion of the development electrode from the point whenthat portion enters the zone in which development will take place to thepoint when that portion leaves the development zone is less than threeminutes for high quality continuous tone xerographic reproductions. Forline copy work, slower speeds are possible.

When two endless belt development electrodes are used, as for example,as in the embodiment shown in Fig. 3, it is preferred that the aerosolof powder particles is sprayed as near to the center as possible. Thiswill allow even distribution of aerosol or cloud under each of thedevelopment electrodes and equally against areas of the surface to bedeveloped.

Erushes or wiper blades used to clean the electrodes may be typesgenerally known to those in the art. For example, nylon brushes, furbrushes, rubber wipers, and the like have been found to produce resultsdesired according to this invention.

While there has been described what at present is considered to be apreferred embodiment of the invention, it is to be understood that manychanges and modifications may be made therein without departing from theessen- 3 tial spirit of the invention. It is intended, therefore, thatthe appended claims cover all modifications as fall within the scope ofthis invention.

What is claimed is:

1. In a xerographic apparatus, the combination comprising a circularcylindrical xerographic plate comprising an outer layer of conductivematerial and an inwardly facing inner layer of photoconductiveinsulating material, means to rotate the cylindrical xerographic plateabout its axis, and a development station within said xerographic plate,said development station comprising a development electrode positioningplate having dimensions corresponding to an area to be developed andhaving a convex surface positioned and conforming to the arc of acylinder concentric to and located within the cylindrical xerographicplate, a conductive endless belt development electrode positioned aroundthe development electrode positioning plate and in area contacttherewith, means to drive the endless belt development electrode tocause continuous movement of the electrode during development whilemaintaining a portion of the electrode against the convex surface of thepositioning plate, the electrode at said positioning plate being spacedapart by a gap from said photoconductive insulating layer of saidxerographic plate, means to supply developer powder to the gap betweenthe surface of the photoconductive insulating layer and'the developmentelectrode at the development station, and cleaning means to clean powderfrom the endless belt development electrode positioned at a pointremoved from the surface of the xerographic plate.

2. In a xerographic apparatus, the combination comprising a cylindricalxerographic plate comprising an outer layer of conductive material andan inwardly facing inner layer of photoconductive insulating material, afirst and a second positioning plate each positioned at a slightdistance from the photoconductive insulating inner layer of thexerographic plate and each adjacent the other, said positioning plateshaving convex surfaces conforming to the arc of a cylinder concentric toand positioned within the cylindrical xerographic plate while spacedapart therefrom, said positioning plates having dimensions correspondingto an area of said xerographic plate to be developed, a first conductiveendless belt development electrode positioned to move through a pathwhich includes area contact with the convex surface of the firstpositioning plate, a second conductive endless belt developmentelectrode positioned to move through a path which includes area contactwith the convex surface of the second positioning plate, said electrodesagainst said positioning plates being spaced apart by a gap from saidphotoconductive insulating layer of said xerographic plate, drive meansto move said electrodes through their respective paths, means to supplydeveloper powder to the gap between the surface of the photoconductiveinsulating layer and the development electrodes at the developmentstation, and cleaning means positioned along the path of movement ofeach endless belt development electrode at a point removed from thesurface of the xerographic plate to clean powder from the endless beltdevelopment electrodes.

3. In a xerographic apparatus, the combination comprising a cylindricalxerographic plate comprising an outer layer of conductive material andan inwardly facing inner layer of photoconductive insulating material, afirst and second positioning plate positioned at a slight distance fromthe photoconductive insulating inner layer of the xerographic plate andeach adjacent the other, said positioning plates having convex surfacesconforming to the arc of a cylinder concentric to and positioned withinthe cylindrical xerographic plate and spaced apart from said xerographicplate, said positioning plates having dimensions corresponding to anarea of said xerographic plate to be developed, a first conductiveendless belt development electrode positioned to move through a pathwhich includes area contact with the convex surface of the firstpositioning plate, a second endless belt development electrodepositioned to move through a path which includes area contact with theconvex surface of the second positioning plate, said electrodes againstsaid positioning plates being spaced apart by a gap from saidphotoconductive insulating layer of said xerographic plate, the paths ofsaid development electrodes further including a region extending fromthe adjacent ends of said positioning plates and in which the electrodesare in a spaced apart relation defining a channel extending to the gapbetween the development electrodes and said photoconductive insulatinglayer of said xerographic plate, drive means to move each of saidelectrodes through their respective paths, powder spray means to sprayan aerosol of powder particles into said channel toward said plate, andcleaning means positioned along the path of movement of each endlessbelt development electrode at a point removed from the surface of thexerographic plate to clean powder from each of said endless beltdevelopment electrodes.

4. In a Xerographic apparatus, the combination comprising a cylindricalxerographic plate comprising an outer layer of conductive material andan inwardly facing inner layer of photoconductive insulating material,means to rotate the cylindrical xerographic plate through variousstations including a charging station to sensitize the photoconductiveinsulating material, an exposure station to form an electrostatic chargepattern on the surface of the photoconductive insulating material, adevelopment station to develop the electrostatic charge pattern withpowder particles and a transfer station to transfer the developed imageto a transfer surface, said development station comprising at least onedevelopment electrode positioning plate positioned within theXerographic plate and having a convex surface shaped to conform to thearc of a cylinder concentric to and positioned within the cylindricalXerographic plate while spaced apart therefrom, the positioning platearea corresponding in dimensions to an area of said xerographic plate tobe developed, an endless belt development electrode positioned aroundeach development electrode positioning plate, means to drive eachendless belt development electrode to cause continuous movement of eachelectrode during development while maintaining a portion of eachelectrode in area contact with the convex surface of its developmentelectrode positioning plate, means to hold each electrode taut tothereby maintain the electrode in close area contact with itspositioning plate, each electrode against each positioning plate beingspaced apart by a gap from said photoconductive insulating layer of saidXerographic plate, means to spray developer powder material to the gapbetween the photoconductive insulating layer and each developmentelectrode, and cleaning means positioned to clean powder from eachendless belt development electrode at a point removed from the surfaceof the xerographic plate.

References Cited in the file of this patent UNITED STATES PATENTS

